Instead of a cell just breaking off from a tumour and travelling through the bloodstream to another organ where it forms a secondary tumour, or metastasis, researchers in the United States have shown that the cancer sends out envoys to prepare the new site.

Intercepting those envoys, or blocking their action with drugs, might help to prevent the spread of cancer or to treat it in patients in which it has already occurred.
   
"We are basically looking at all the earlier steps that are involved in metastasis that we weren't previously aware of. It is complex, but we are opening the door to all these things that occur before the tumour cell implants itself," said Professor David Lyden of Cornell University in New York.

"It is a map to where the metastasis will occur," he added in an interview. 
 
Colonisation of organs

Cancer's ability to colonise other organs is what makes the disease so deadly.

Once the cancer has spread beyond its original site it is much more difficult to treat.
   
In research reported in the journal Nature, Lyden and his colleagues describe what happens before the arrival of the cancerous cells at the new site.
   
"The authors show that tumour cells can mobilise normal bone marrow cells, causing them to migrate to particular regions and change the local environment so as to attract and support a developing metastasis," Patricia Steeg, of the National Cancer Institute in Bethesda, Maryland, said in a commentary. 
   

"This is the first time anyone has discovered what we call the pre-metastatic niche"

Professor David Lyden, Cornell University in New York

Cells at the site of the metastasis multiply and produce a protein called fibronectin, which acts like a glue to attract and trap the bone marrow cells to create a landing pad or nest for the cancer cells.

"These nests provide attachment factors for the tumour cells to implant and nurture them. It causes them not only to bind but to proliferate. Once that all takes place we have a fully formed metastatic site or secondary tumour," said Lyden.

"This is the first time anyone has discovered what we call the pre-metastatic niche."

Without the landing pad, the cancerous cell could not colonise the organ.

In animal and laboratory studies, the scientists looked at how breast, lung and oesophageal cancer spread.

The envoys from the tumour determine the site of the secondary site.
   
Lyden said measuring the number of special bone marrow cells circulating in the body could help to determine whether a cancer is likely to spread.
   
"This opens up the door to new concepts of how metastasis is taking place. If we can understand all these multiple processes we can develop new drugs that block each step. That way we have a much better future than just trying to treat the tumour cell, which is almost like a last step in this process," he added.